Making a scene, using Blender render but want to add tree's that are done in cycles
Perhaps you could add a tree image with a transparent backdrop. Then in the nodes remove the backdrop with a transparent node, and apply some different shaders such as specular and bump or normal maps to give the realism effect. This is what is used in most games as it uses minimalist faces which saves time in your final render, However they are used for distance scenes. This is the only other way of creating a tree that i can think of without creating a 3D tree, whether that be sculpted or generated with the Tree plugin.
Hope this helps Mate.